1. Field of the Invention
The present invention relates to a mobile robot, and more particularly, to an apparatus and method of estimating the position and orientation of a mobile robot in dark environment or an environment having conditions resulting in changes of illumination.
2. Description of the Related Art
There are generally four methods of estimating the position and orientation of a mobile robot by using artificial beacons, or guides. A first method uses reflecting objects and a vision system. An example of this method is disclosed in U.S. Pat. No. 5,051,906, wherein an automatic guided vehicle (AGV) travels along a hallway using retro-reflective stripes attached to the ceiling. The orientation and position of the AGV is determined when the AGV travels along a long axis of the hallway. A second method uses only reflectors. Examples of this method are disclosed in U.S. Pat. No. 5,812,267 and U.S. Pat. No. 5,467,273. A third method uses a vision system and specific marks instead of reflectors. Examples of this method are disclosed in U.S. Pat. No. 5,525,883, U.S. Pat. No. 5,911,767, and U.S. Pat. No. 6,496,754. In U.S. Pat. No. 5,911,767, a mobile robot is localized by setting circles as coded signs and recognizing the coded signs. In particular, the robot's position and orientation are obtained using a ratio of two diameters of two concentric circles related to the coded signs discriminated from the environment. In U.S. Pat. No. 6,496,754, a location of a robot is detected using a base mark including two marks, and a shape of an obstacle is recognized using a laser beam. A fourth method uses a vision system and a light source instead of reflectors. An example of this method is disclosed in U.S. Pat. No. 4,797,557.
However, in the conventional methods described above, it is impossible to estimate the global position and orientation of a mobile robot in an entire environment wherein the mobile robot is capable of moving, and the accuracy of estimating the position and orientation varies according to environmental conditions, such as changes in illumination. Accordingly, it is difficult to use the conventional methods in a general indoor environment, such as a house.